Flame monitoring device and flame monitoring program

ABSTRACT

To detect a sign of a flame failure that cannot be detected by monitoring a flame voltage and a flame current, a flame monitoring device is provided that includes an information acquisition unit that sequentially acquires a flame level indicating frequency of discharge of a flame detector caused by a flame of a main burner, and a flame level monitoring unit that monitors the flame level sequentially acquired by the information acquisition unit. The flame level monitoring unit detects a sign of a flame failure of the flame by detecting an occurrence of a specific period during which a state in which the flame level is less than a predetermined threshold value continues for a length of time equal to or more than a predetermined period and less than a flame response period.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of foreign priority to Japanese Patent Application No. JP 2022-121866 filed on Jul. 29, 2022, the disclosure of which is herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The present disclosure relates to a flame monitoring device and a flame monitoring program.

Japanese Patent Application Publication No. JP 2019-060573 A (“JP '573”) discloses a technique for monitoring a flame voltage or a flame current indicating an active degree of a flame of a burner for each of a plurality of sub-sequences (in JP '573, “pilot ignition (trial)”, “pilot-only”, “main lighting”, and “main stabilization”) constituting a combustion sequence. In this technique, when the flame voltage or the flame current deviates from a predetermined range defined for each sub-sequence, it is notified that a malfunction, that is, a sign of a flame failure has occurred in the combustion device.

BRIEF SUMMARY OF THE INVENTION

However, by monitoring the flame voltage or the flame current as in the technique disclosed in JP '573, only a part of the various signs of the flame failure can be detected. For example, flame lifting, which is considered to be a sign of a flame failure, cannot be detected by monitoring the flame voltage or the flame current.

The present disclosure has been made in view of the above points, and an aspect thereof is to detect a sign of a flame failure that cannot be detected by monitoring a flame voltage and a flame current.

In order to solve the above problem, a flame monitoring device according to the present disclosure includes: an information acquisition unit configured to sequentially acquire a flame level indicating frequency of discharge of a flame detector caused by a flame of a burner; and a flame level monitoring unit configured to monitor the flame level sequentially acquired by the information acquisition unit. The flame level monitoring unit detects a sign of a flame failure of the flame by detecting an occurrence of a specific period during which a state in which the flame level is less than a predetermined threshold value continues for a length of time more than or equal to a predetermined first period and less than a second period, and the second period is a period having a length of time equal to or less than a period from an occurrence of the flame failure of the flame to the detection of the flame failure in a combustion system that controls the burner when it is assumed that the flame failure occurs.

As an example, the flame level monitoring unit executes a process of notifying that the sign is detected when the occurrence of the specific period is detected.

As an example, the flame level monitoring unit executes a process of notifying that the sign is detected when the number of occurrences of the specific period per certain period is larger than a predetermined number of times larger than or equal to two.

As an example, the information acquisition unit sequentially acquires flow rates of fuel and air that are supplied to the burner, and the flame level monitoring unit notifies the detection of the sign along with flow rate information indicating a relation between the flow rates of fuel and air in at least one of the specific periods and a certain period traced back from the specific period based on the flow rates of fuel and air that are sequentially acquired by the information acquisition unit.

As an example, the information acquisition unit sequentially acquires combustion information including at least the flame level in the combustion system. The flame level monitoring unit is configured to: learn a relation between presence or absence of the occurrence of the flame failure and the combustion information by using, as training data, a variation in combustion information in a period traced back by a predetermined time from the actually occurring flame failure and a variation in combustion information for the predetermined time when no flame failure occurs from the combustion information sequentially acquired by the information acquisition unit; and derive a possibility of the occurrence of the flame failure based on the variation in combustion information for the predetermined time from the combustion information sequentially acquired by the information acquisition unit and the learned relation, and execute a process based on the derived possibility.

As an example, the flame level monitoring unit learns the relation by using a variation in combustion information in a period traced back by the predetermined time from the specific period actually generated from the combustion information sequentially acquired by the information acquisition unit as the variation in combustion information in a period traced back by the predetermined time from the flame failure.

As an example, the process based on the possibility includes at least one of a process of notifying the possibility, a process of notifying that the possibility is larger than a predetermined value when the possibility is larger than the predetermined value, and a process of stopping fuel supply to the burner when the possibility is larger than the predetermined value.

A flame monitoring program according to the present disclosure causes a computer to execute: an information acquisition step of sequentially acquiring a flame level indicating frequency of discharge of a flame detector caused by a flame of a burner; and a flame level monitoring step of monitoring the flame level sequentially acquired by the information acquisition step. In the flame level monitoring step, a sign of a flame failure of the flame is detected by detecting an occurrence of a specific period during which a state in which the flame level is less than a predetermined threshold value continues for a length of time more than or equal to a predetermined first period and less than a second period, and the second period is a period having a length of time equal to or less than a period from an occurrence of the flame failure of the flame to the detection of the flame failure in a combustion system that controls the burner when it is assumed that the flame failure occurs.

According to the present disclosure, a sign of a flame failure that cannot be detected by monitoring a flame voltage and monitoring a flame current can be detected.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a configuration diagram of a heating system including a flame monitoring device according to an embodiment of the present disclosure.

FIG. 2 is a flowchart of a combustion sequence executed by a combustion control device.

FIG. 3 is a graph showing a relation between a flame voltage and a flame level.

FIG. 4 is a hardware configuration diagram of the flame monitoring device.

FIG. 5 is a partial configuration diagram of the flame monitoring device.

FIG. 6 is a flowchart of a flame monitoring process.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment of the present disclosure and modifications thereof will be described with reference to the drawings.

Embodiment

As shown in FIG. 1 , a flame monitoring device 20 according to an embodiment of the present disclosure is used in a combustion system 10. The flame monitoring device 20 monitors a flame level FL, which will be described later, of a flame of a main burner 42 when a combustion device 30 of the combustion system 10 combusts a fuel gas, and detects and notifies of a sign of a flame failure due to deterioration of equipment of the combustion device 30 or the like. The sign of the flame failure detected in this embodiment includes lifting and flashback of the flame.

The combustion system 10 includes, in addition to the flame monitoring device 20, the combustion device 30 that performs combustion, a combustion control device 71 that controls the combustion device 30, and a temperature regulator 75 that gives various instructions to the combustion control device 71. Hereinafter, the combustion device 30, the combustion control device 71, and the temperature regulator 75 will be described first, and then the flame monitoring device 20 will be described.

The combustion device 30 includes a combustion equipment 40, a fuel supply system 50, an air supply system 60, a control motor M, and an opening degree sensor MS.

The combustion equipment 40 combusts a fuel gas inside a combustion chamber R. The combustion equipment 40 includes a combustion furnace 41 that forms the combustion chamber R, the main burner 42 that combusts the fuel gas to heat the inside of the combustion chamber R, a pilot burner 43 that combusts fuel to light the main burner 42, and an ignition device (an igniter) 44 that ignites the pilot burner 43.

The combustion equipment 40 further includes a flame detector 45 that detects flames of the main burner 42 and the pilot burner 43, and a temperature sensor 46 that detects a temperature inside the combustion chamber R. The flame detector 45 detects the flame by detecting electromagnetic waves (for example, ultraviolet rays) radiated from the flames of the main burner 42 or the pilot burner 43.

The fuel supply system 50 supplies the fuel gas from the outside to the combustion equipment 40. The fuel supply system 50 includes a fuel flow path 51 through which the fuel gas to be supplied to the combustion equipment 40 flows. The fuel flow path 51 includes a main flow path 51A to which the fuel gas is supplied from the outside, and a first flow path 51B and a second flow path 51C that are branched from the main flow path 51A. The first flow path 51B is connected to the main burner 42, and the second flow path 51C is connected to the pilot burner 43.

The fuel supply system 50 further includes main valves 54A and 54B provided in the first flow path 51B and pilot valves 54C and 54D provided in the second flow path 51C. The main valves 54A and 54B open and close the first flow path 51B. The pilot valves 54C and 54D open and close the second flow path 51C. The fuel supply system 50 further includes a damper 55 that is provided in the main flow path 51A and used to adjust a flow rate of fuel, and a fuel flow meter 56 that detects a flow rate of fuel flowing through the first flow path 51B, that is, supplied to the main burner 42.

The air supply system 60 supplies air to the combustion equipment 40. The air supply system 60 includes an air flow path 61 that supplies the air to the main burner 42 of the combustion equipment 40 and a blower 62 that causes the air to flow through the air flow path 61. The air supply system 60 further includes a damper 65 that is provided in the air flow path 61 and used to adjust a flow rate of air, and an air flow meter 66 that detects the flow rate of air flowing through the air flow path 61, that is, supplied to the main burner 42.

The damper 55 used to adjust the flow rate of fuel and the damper 65 used to adjust the flow rate of air are operated by the control motor M to control opening degrees of the fuel flow path 51 (the first flow path 51B) and the air flow path 61. The dampers 55 and 65 operate while being interlocked with each other by a linkage mechanism. Accordingly, the opening degrees of the dampers 55 and 65 are interlocked. The dampers 55 and 65 may be interlocked with each other by another configuration. For example, the damper 65 may be a pressure equalizing valve into which an air pressure in the air flow path 61 of the air supply system 60 is introduced. The damper 65, which is a pressure equalizing valve, operates such that the air pressure in the air flow path 61 and a fuel pressure in the first flow path 51B of the fuel flow path 51 are made uniform.

The opening degrees of the dampers 55 and 65 are interlocked such that a fuel-air ratio, which is a ratio of the fuel to the air supplied to the main burner 42, is maintained at a desired ratio. Amounts of the fuel and air supplied to the main burner 42 are adjusted by the opening degrees of the dampers 55 and 65, thereby adjusting an active degree of a flame, more specifically, a flame strength of each burner. As a result, a heating temperature is controlled under which the combustion chamber R or a workpiece provided in the combustion chamber R is heated.

The control motor M is provided with the opening degree sensor MS that detects the opening degrees of the dampers 55 and 65 by detecting rotation angles of a rotating shaft or the like. The opening degrees detected by the opening degree sensor MS are used as feedback values when the control motor M is feedback-controlled to control the opening degrees of the dampers 55 and 65.

The combustion control device 71 includes various computers such as a programmable logic controller (PLC) and a personal computer. The combustion control device 71 may also include central processing units (CPUs) that constitute the computers, as well as various circuits (analog circuits and the like) capable of implementing operations described later. The combustion control device 71 is also referred to as a burner controller.

The combustion control device 71 controls the combustion device 30 according to a predetermined combustion sequence in FIG. 2 to heat the inside of the combustion chamber R. It is assumed that the valves 54A to 54D of the fuel supply system 50 are closed at the start of the combustion sequence.

During pre-purging (step S1), the combustion control device 71 drives the control motor M, controls the damper 65 to a high opening degree position, and operates the blower 62 of the air supply system 60. Accordingly, fresh air is blown into the combustion chamber R via the main burner 42.

After the pre-purging, the combustion control device 71 performs pilot ignition (step S2). During the pilot ignition, the combustion control device 71 first controls the dampers 55 and 65 to a low opening degree position. Then, the combustion control device 71 controls the pilot valves 54C and 54D of the fuel supply system 50 to an open state to start fuel supply to the pilot burner 43, and operates the ignition device 44 to generate an ignition spark. Accordingly, the pilot burner 43 is ignited. When the flame detector 45 detects ignition of the pilot burner 43, the combustion control device 71 performs pilot-only (step S3). During the pilot-only, the combustion control device 71 is on standby for a predetermined period to stabilize the flame of the pilot burner 43.

After the pilot-only, the combustion control device 71 performs main lighting (step S4) in which the main valves 54A and 54B of the fuel supply system 50 are controlled to an open state to start fuel supply to the main burner 42. Accordingly, the main burner 42 is lighted using the flame of the pilot burner 43 as seed light. After a certain period has elapsed since the main valves 54A and 54B are controlled to the open state, the combustion control device 71 determines that the main lighting is completed and performs main stabilization (step S5). During the main stabilization, the pilot valves 54C and 54D of the fuel supply system 50 are closed and the flame of the pilot burner 43 is extinguished. Furthermore, during the main stabilization, a standby is also performed for the flame of the main burner 42 to stabilize.

After the main stabilization, the combustion control device 71 shifts to steady combustion (step S6). The inside of the combustion chamber R is heated by steady combustion of the main burner 42. During the steady combustion, the combustion control device 71 controls the opening degrees of the dampers 55 and 65 via the control motor M to control flow rates of air and fuel to the main burner 42, and accordingly controls firepower, that is, the active degree of the flame of the main burner 42. The combustion control device 71 closes the main valves 54A and 54B of the fuel supply system 50 to extinguish the flame of the main burner 42 at a timing of the end of the steady combustion. A post-purge may be performed after the steady combustion.

Referring back to FIG. 1 , the temperature regulator 75 instructs the combustion control device 71 to start the combustion sequence and end the steady combustion (an end timing of the combustion sequence). Further, the temperature regulator 75 uses a temperature detected by the temperature sensor 46 as a feedback value to instruct the combustion control device 71 to bring the temperature inside the combustion chamber R to a target temperature. The temperature regulator 75 indicates the flow rates of fuel and air during the steady combustion, and the like, based on a relation between the feedback value and the target temperature. When the temperature regulator 75 indicates the flow rates of fuel and air, the temperature regulator 75 supplies the flow rates to the combustion control device 71 as target values. The combustion control device 71 derives a target opening degree from the supplied target values, and performs feedback control on the control motor M using the opening degrees from the opening degree sensor MS as feedback values such that the opening degrees of the dampers 55 and 65 become the target opening degrees. The combustion control device 71 may control the target opening degrees by feedback control using, as feedback values, the amounts of fuel and air to the main burner 42 that are respectively detected by the flow meters 56 and 66.

The flame detector 45 provided in the combustion equipment 40 includes a discharge tube (for example, an ultraviolet ray tube) that discharges when receiving electromagnetic waves (for example, ultraviolet rays) radiated from a flame. A discharge current generated by the discharge is input to the combustion control device 71.

The combustion control device 71 integrates a potential difference between both ends of a resistor through which the discharge current from the flame detector 45 flows to generate a flame voltage FV (which may be a flame current, the same applying hereinafter) representing the active degree of the flame. This integration is performed by, for example, an integration circuit. The flame voltage FV has a voltage value that varies between 0 V and 5 V. In the above combustion sequence and the like, the combustion control device 71 monitors the flame voltage FV. The combustion control device 71 detects the presence (lighting or ignition) of a flame when the flame voltage FV becomes a predetermined threshold value FVth or more. The combustion control device 71 detects flame extinguishment when the flame voltage FV becomes less than the threshold value FVth. Extinguishment means that the flame is extinguished. The extinguishment includes extinguishment caused by closing the main valves 54A and 54B and a flame failure caused by unintentional extinguishment of a flame while the main valves 54A and 54B are open.

When the flame voltage FV is less than the threshold value FVth and the extinguishment (that is, the flame failure) is detected in sub-sequences such as main stabilization and steady combustion of the combustion sequence, the combustion control device 71 supplies a closing signal for closing a valve to the main valves 54A and 54B. Accordingly, the supply of the fuel gas is stopped. Different threshold values may be used for detecting the presence of the flame and for detecting flame extinguishment.

Further, the combustion control device 71 generates a discharge pulse signal (for example, a voltage signal) that indicates discharge based on the potential difference or the like. The combustion control device 71 generates the flame level FL, which is a numerical value indicating frequency of discharge of the discharge tube of the flame detector 45, from the discharge pulse signal. Specifically, the combustion control device 71 counts, based on the discharge pulse signal, the number of discharge pulses per certain time (for example, 0.1 seconds), that is, the number of discharge times N. The combustion control device 71 derives the flame level FL based on the counted number of discharge times N. A method for deriving the flame level FL may be any method, and here the flame level FL is derived by the following Equation (1). In the equation, Nmax is the maximum number of discharge times per certain time described above.

FL=(N/N max)*100  (1)

The flame level FL is supplied from the combustion control device 71 to the flame monitoring device 20 and monitored by the flame monitoring device 20. Here, the flame level FL is represented by percentage, and may be represented by N/Nmax or N alone.

Both the flame voltage FV and the flame level FL are numerical values that indicate the active degree (an intensity here) of the flame. FIG. 3 shows temporal changes in the flame voltage FV and the flame level FL from lighting of the main burner 42 to the flame failure of the flame. For ease of understanding, FIG. 3 is a schematic diagram in which the main burner 42 is lighted independently without using the flame of the pilot burner 43 as seed light.

As shown in FIG. 3 , the flame voltage FV is derived as a continuous value, and the flame level FL is derived as a discrete value for each certain period described above. Since the flame voltage FV is a value obtained by the above integration, responsiveness of the flame voltage FV to changes (changes in an ultraviolet ray amount or discharge current) in the flame is slower than that of the flame level FL. Accordingly, even if flame lifting due to temporary interruption of the electromagnetic waves incident on the flame detector 45, flame flashback, or the like occurs (for example, refer to a period of a timing T3 to a timing T4), the flame voltage FV does not fall below the threshold value FVth, which is a criterion for determining the extinguishment. Accordingly, the flame voltage FV is generated so as not to erroneously detect the above lifting or the like as an extinguishment. In other words, with the flame voltage FV, the above lifting or the like cannot be detected.

A period from a first timing when the flame level FL is less than a threshold value FLth to a second timing when the flame voltage FV is less than the threshold value FVth for detecting the extinguishment (mainly, a flame failure) is also referred to as a flame response period Tfr. The first timing can also be said to be a timing when the flame failure actually occurs. The second timing can also be said to be a timing when the flame failure is detected by the combustion control device 71. For this reason, it can be said that the flame response period Tfr is a response period from an occurrence of the flame failure to the detection of the flame failure in the combustion system 10 that controls the main burner 42 when it is assumed that a flame failure of the flame has occurred. The flame response period Tfr is adjusted by a time constant or the like of the integration circuit that derives the flame voltage FV, and is set as a known value. As described above, upon detection of the flame failure, the closing signal is supplied to the main valves 54A and 54B to start a closing operation of the valves. Therefore, it can be said that a detection timing of the flame failure is a start timing of stopping fuel supply to the main burner 42.

The flame level FL is sensitive to a change in the ultraviolet ray amount (that is, the discharge current). Therefore, by setting the predetermined threshold value FLth for the flame level FL, the flame lifting due to temporary interruption of the electromagnetic waves incident on the flame detector 45, the flame flashback, or the like can be detected (details will be described later). In FIG. 3 , the flame level FL is less than the threshold value FLth in a period of the timing T3 to the timing T4 having a length of time less than the flame response period Tfr, and the above lifting or the like may occur in this period. In a period when the flame level FL is less than the threshold value FLth in less than the flame response period Tfr, a flame failure is not detected, and the main valves 54A and 54B are not closed.

The flame monitoring device 20 shown in FIG. 1 includes various computers such as a personal computer. As shown in FIG. 4 , the flame monitoring device 20 includes a processor 21 such as a CPU, a random access memory (RAM) 22 that functions as a main memory of the processor 21, and a non-volatile storage device 23 that stores a flame monitoring program executed by the processor 21. The storage device 23 also stores various types of data used in the following processes. The flame monitoring device 20 further includes a display 24 that displays various screens to be described later, an operation device 25 operated by a user, and a communication module 26 that causes the processor 21 to communicate with the combustion control device 71 and the temperature regulator 75.

In this embodiment, the processor 21 functions as an information acquisition unit 21A and a flame level monitoring unit 21B shown in FIG. 5 by executing the flame monitoring program stored in the storage device 23.

The information acquisition unit 21A sequentially acquires the flame level FL from the combustion control device 71 via the communication module 26. The flame level FL may be recorded in the RAM 22 or the storage device 23 in chronological order.

The flame level monitoring unit 21B detects and notifies of a sign of a flame failure of the flame by monitoring the flame level FL acquired by the information acquisition unit 21A.

The flame level monitoring unit 21B monitors an occurrence of a specific period T. During the specific period T, a state in which the flame level FL is less than the predetermined threshold value FLth continues for a length of time equal to or more than a predetermined period Tth (for example, 2 seconds) and less than the flame response period Tfr. In the monitoring, the occurrence of the specific period T is detected by the flame level monitoring unit 21B. When the occurrence of the specific period T is detected, it is considered that detection signals (the discharge current) of the electromagnetic waves representing the flame are temporarily interrupted and recovered, and the flame lifting, the flame flashback, or the like which is not a flame failure is generated. A length of time of the predetermined period Tth is set as a period for detecting the lifting or the like.

The flame lifting, the flame flashback, and the like are caused by a malfunction of the linkage mechanism, fuel-air ratio deviation due to damage or clogging of an air flow path or a fuel gas flow path, and the like, and thus can be said to be signs of flame failure. Accordingly, the flame level monitoring unit 21B detects the flame lifting, the flame flashback, and the like, that is, the signs of flame failure by detecting the occurrence of the specific period T. Here, these signs of flame failure cannot be detected by monitoring the flame voltage FV (or the flame current) as described above. Accordingly, the flame level monitoring unit 21B can detect signs of flame failure that cannot be detected by monitoring the flame voltage FV (or the flame current).

The flame level monitoring unit 21B executes, for example, a flame monitoring process shown in FIG. 6 . The flame monitoring process is executed every time the flame level FL is acquired by the information acquisition unit 21A in the main stabilization and the steady combustion in the combustion sequence. The start and end of the main stabilization and the steady combustion are notified from the combustion control device 71.

The flame level monitoring unit 21B determines whether the flame level FL acquired this time is less than the threshold value FLth (for example, 5%) (step S11). When the flame level FL is less than the threshold value FLth (step S11; Yes), the flame level monitoring unit 21B increments a timer value of a measurement timer, which is provided in the RAM 22 and measures a continuation period Tk in a state in which the flame level FL is less than the threshold value FLth, by +1 (step S12), and ends the flame monitoring process.

When the flame level FL is larger than or equal to the threshold value FLth (step S11; No), the flame level monitoring unit 21B determines whether the continuation period Tk indicated by the timer value of the measurement timer is more than or equal to the predetermined period Tth (step S13). When a determination result is negative (step S13; No), the continuation period Tk is less than the predetermined period Tth, the sign of the flame failure does not occur, and the specific period T does not occur. In this case, the flame level monitoring unit 21B resets the timer value of the measurement timer to 0 (step S14), and terminates the flame monitoring process.

If the continuation period Tk reaches the flame response period Tfr, a flame failure has occurred. In this case, in the combustion control device 71, a process of closing the main valves 54A and 54B and the like are performed, and the combustion sequence is forcibly terminated. The combustion control device 71 notifies the flame level monitoring unit 21B of the forced termination. In this case, the flame level monitoring unit 21B resets the timer value of the measurement timer. Accordingly, the continuation period Tk indicated by the timer value of the measurement timer is not more than the flame response period Tfr. Therefore, when the continuation period Tk indicated by the timer value of the measurement timer is more than or equal to the predetermined period Tth, the continuation period Tk is necessarily less than the flame response period Tfr.

When the continuation period Tk is more than or equal to the predetermined period Tth (step S13; Yes), as described above, the continuation period Tk is also less than the flame response period Tfr, and thus the flame level monitoring unit 21B determines that the occurrence of the specific period T, that is, the sign of the flame failure is detected, and records the determination (step S15). Further, the flame level monitoring unit 21B executes a notification process of notifying the user of the combustion system 10 that the sign of the flame failure is detected based on the recorded recording content (step S16), and resets the measurement timer (step S17).

In step S15, the flame level monitoring unit 21B turns on a sign flag provided in the RAM 22. In step S16, when the sign flag is turned on, the flame level monitoring unit 21B displays, on the display 24, a predetermined message (such as “A sign of a flame failure (lifting or flashback) is detected. Please check fuel-air ratio or the like.”) indicating that the sign of the flame failure is detected.

In step S15, the flame level monitoring unit 21B may set a counter that counts the number of occurrences of the sign provided in the RAM 22 to +1. In step $16, when a value of the counter is equal to or larger than a predetermined value, the flame level monitoring unit 21B may display, on the display 24, a predetermined message that the sign of the flame failure is detected. The predetermined value may be once or a plurality of times. When the predetermined value is the plurality of times, the value of the counter may be reset periodically (for example, every day or every week). Accordingly, when the number of occurrences of the specific period T per certain period, that is, the number of occurrences of the sign is equal to or larger than the predetermined value equal to or larger than two, it is displayed that the sign of the flame failure is detected. The message to be displayed may include a message that a possibility of the flame failure is high.

As described above, in this embodiment, the information acquisition unit 21A sequentially acquires the flame level FL indicating frequency of discharge of the flame detector 45 caused by the flame of the main burner 42. Further, the flame level monitoring unit 21B monitors the sequentially acquired flame level FL. In particular, the flame level monitoring unit 21B detects a sign of the flame failure such as flame lifting or flame flashback by detecting an occurrence of the specific period T. During the specific period T, a state in which the flame level FL is less than the predetermined threshold value FLth continues for a length of time equal to or more than the predetermined period Tth set in advance and less than the flame response period Tfr. Accordingly, the sign of the flame failure that cannot be notified of by monitoring the flame voltage FV or the flame current is detected.

Further, when the occurrence of the specific period T is detected, the flame level monitoring unit 21B executes a process of notifying that the sign of the flame failure of the flame is detected. Accordingly, the user can grasp the sign of the flame failure. Accordingly, the user can check and repair the combustion device 30, and as a result, the occurrence of the flame failure is prevented.

The flame level monitoring unit 21B may execute a process of notifying that the sign of the flame failure is detected when the number of occurrences of the specific period T per certain period is larger than a predetermined number of times larger than or equal to two, as described above. Accordingly, when the frequency of lifting, flashback, or the like is increased, that is, the possibility of the flame failure is increased, it is possible to notify that the sign of the flame failure is detected.

MODIFICATIONS

A configuration of the above embodiment can be freely changed. Modifications are exemplified below. The modifications can be combined at least partially.

Modification 1

The information acquisition unit 21A may function as a data collector or the like, and may sequentially acquire flow rates of fuel and air that are supplied to the main burner 42. The information acquisition unit 21A communicates with the combustion control device 71, periodically acquires the flow rates of fuel and air to the main burner 42 that are respectively detected by the flow meters 56 and 66, and stores the acquired flow rates of fuel and air in the storage device 23 in chronological order. The flow rates of fuel and air may be expressed by a valve opening degree detected by the opening degree sensor MS, an operation amount input to the control motor M, or the like.

When displaying that the above sign is detected, the flame level monitoring unit 21B may acquire the flow rates of fuel and air in at least one of the specific periods T and a certain period traced back from the specific period T, among the flow rates of fuel and air that are acquired by the information acquisition unit 21A and that are stored in the storage device 23. The flame level monitoring unit 21B may display, on the display 24, flow rate information indicating a relation between the acquired flow rates of fuel and air along with the message that the above sign is detected. The flow rate information includes, for example, any one of a graph indicating a variation in the flow rate of fuel and a variation in the flow rate of air, a ratio between the flow rate of fuel and the flow rate of air at a certain timing, a variation in the ratio between the flow rate of fuel and the flow rate of air, and the flow rate of fuel and the flow rate of air themselves. According to such a configuration, when the sign of the flame failure occurs, it is possible to allow the user to grasp which of the flow rate of fuel and the flow rate of air has a problem or how much the fuel-air ratio deviates.

Modification 2

The information acquisition unit 21A may function as the above data collector to sequentially acquire combustion information including at least the flame level FL in the combustion device 30. The combustion information may include, in addition to the flame level FL, one or a plurality of physical quantities that can vary according to a flame state of the burner. Examples of the physical quantities include a flow rate of air, a flow rate of fuel, a combustion amount set value, and an air ratio of an air-fuel mixture gas. The combustion information may include only the flame level FL. The air ratio of the air-fuel mixture gas is calculated based on the flow rate of air and the flow rate of fuel. The combustion amount set value includes, for example, a flow rate of fuel and a flow rate of air in the steady combustion that are included in the instruction given to the combustion control device 71 by the temperature regulator 75.

The flame level monitoring unit 21B may learn a relation between the presence or absence of the occurrence of the flame failure and a variation in combustion information by using, as training data, a variation in combustion information in a period traced back by a predetermined time (for example, 10 minutes) from the actually occurring flame failure and a variation in combustion information for the predetermined time when no flame failure occurs based on the combustion information (in particular, the flame level FL) sequentially acquired by the information acquisition unit 21A.

For example, the information acquisition unit 21A records the acquired combustion information in the storage device 23 in chronological order along with an acquisition time. The flame level monitoring unit 21B acquires, from the combustion control device 71, a time when a flame failure has occurred, and acquires, based on the acquired time, the combustion information in a period traced back by the predetermined time from the flame failure as training data in which a correct answer is defined as the flame failure. Further, the flame level monitoring unit 21B acquires combustion information in any period (which may be designated by the user) in which no flame failure has occurred (further, when no sign of a flame failure is generated) as training data in which a correct answer is defined as a non-flame failure. The flame level monitoring unit 21B performs machine learning by any learning method based on the training data, and learns the relation between the presence or absence of the occurrence of the flame failure and the variation in the flame level. As the learning method, for example, a learning method such as a support vector machine or a random forest is used. The relation may include information such as how many seconds a low level of the flame level FL continues to cause a high possibility of the occurrence of a flame failure, and how high a frequency of the low level is to cause a high possibility of the occurrence of a flame failure. The relation may be a model such as a support vector machine or a random forest in which a variation in the received combustion information is labeled as either a flame failure or a non-flame failure.

The flame level monitoring unit 21B may derive a possibility of an occurrence of a flame failure in the future based on the variation in the combustion information for the predetermined time from the combustion information sequentially acquired by the information acquisition unit 21A and the learned relation. Further, the flame level monitoring unit 21B may execute a process based on the derived possibility.

The flame level monitoring unit 21B labels the variation in the combustion information for the predetermined time as either a flame failure or a non-flame failure based on the relation. At this time, the flame level monitoring unit 21B derives a possibility (for example, 45 percent of an occurrence of a flame failure) of an occurrence of a flame failure from the labeling.

According to the configuration described above, it is possible to obtain a possibility of an occurrence of a flame failure in which a phenomenon (lifting or the like) that cannot be grasped by the flame voltage FV or the flame current is defined as a sign.

The flame level monitoring unit 21B may execute a process of displaying the possibility on the display 24 as the above-described process. Instead of or in addition to the process, the flame level monitoring unit 21B may execute, as the above-described process, a process of notifying that the possibility of the flame failure is high by displaying the possibility on the display 24 when the possibility is larger than a predetermined value. Instead of or in addition to this process, the flame level monitoring unit 21B may execute, as the above-described process, a process of stopping fuel supply to the main burner 42 when the possibility is larger than the predetermined value. The process of stopping fuel supply to the main burner 42 includes a process of instructing the combustion control device 71 to supply fuel to the main burner 42. Accordingly, it is possible to notify the user of the combustion system 10 of the possibility of the flame failure in the near future, and to prevent an actual flame failure by stopping the combustion sequence when the possibility of the flame failure is high.

Since flame failures rarely occur, there is usually little training data in which the correct answer is defined as the flame failure. Here, the flame level monitoring unit 21B may perform the learning by using a variation in combustion information in a period traced back by the predetermined time from the specific period T that actually occurs from the combustion information sequentially acquired by the information acquisition unit 21A as the training data in which the correct answer is defined as the flame failure. Accordingly, it is possible to solve a shortage of the training data. In order to obtain more training data, the information acquisition unit 21A may collect the combustion information from another combustion system (particularly, a combustion system having a combustion device of the same type as the above combustion device 30) or the like along with occurrence information on the flame failure and the specific period T, and the flame level monitoring unit 21B may use the combustion information acquired from another combustion system as training data.

In this modification, the sign of the flame failure of the flame need not be detected. That is, the flame monitoring device 20 may include an information acquisition unit that sequentially acquires combustion information including at least a flame level indicating frequency of discharge of a flame detector caused by a flame of a burner, and a monitoring unit that monitors the combustion information sequentially acquired by the information acquisition unit. The monitoring unit may learn a relation between the presence or absence of the occurrence of the flame failure and a variation in combustion information by using, as training data, a variation in combustion information in a period traced back by a predetermined time from the actually occurring flame failure and a variation in combustion information for the predetermined time when no flame failure occurs based on the combustion information sequentially acquired by the information acquisition unit, may derive a possibility of the occurrence of the flame failure based on the variation in the combustion information for the predetermined time from the combustion information sequentially acquired by the information acquisition unit and the learned relation, and may execute a process based on the derived possibility.

Modification 3

An upper limit of the specific period T is the flame response period Tfr in the above description, and may be a period shorter than the flame response period Tfr. In this case, in step S13 in FIG. 6 , the flame level monitoring unit 21B may determine whether the continuation period Tk is within a range more than or equal to the predetermined period Tth and less than the shorter period.

Modification 4

A configuration of the combustion system 10 may be freely set. For example, instead of or in addition to the display 24, the flame level monitoring unit 21B may display the detection of a sign, a possibility of an occurrence of a flame failure, and the like on a display device outside the flame monitoring device 20, for example, a terminal of a user of the combustion system 10. Accordingly, the user may be notified of the detection of a sign, the possibility of an occurrence of a flame failure, and the like. The notification to the user may be an audio output or the like. The flame level monitoring unit 21B may only output, to an external device, the detection of a sign, the possibility of an occurrence of a flame failure, or the like.

A hardware configuration of the flame monitoring device 20 may also be freely set. The flame monitoring device 20 may be formed as a gateway that connects the combustion control device 71 and the temperature regulator 75 to other external devices. At least a part of the information acquisition unit 21A and the flame level monitoring unit 21B may include various logic circuits such as an application specific integrated circuit (ASIC) and a field-programmable gate array (FPGA). At least a part of the information acquisition unit 21A and the flame level monitoring unit 21B may be provided to the combustion control device 71 or the temperature regulator 75. The information acquisition unit 21A may acquire a discharge current from the flame detector 45 and derive the flame voltage FV and the flame level FL based on the acquired discharge current to acquire the flame voltage FV and the flame level FL. The flame monitoring device 20 may be a server computer, a cloud computer, or the like. In the flame monitoring device 20 serving as a server computer or a cloud computer, preferably, the information acquisition unit may collect the above combustion information (see Modification 2) in a plurality of combustion systems having the same type of combustion device along with occurrence information on the flame failure or the like, and the monitoring unit may perform the machine learning (see Modification 2) based on the above training data based on the collected combustion information. Accordingly, machine learning is performed using a large number of pieces of training data, and learning accuracy is improved.

The above devices such as the flame monitoring device 20 include systems in each of which components of the system are separately housed in a plurality of housings in addition to devices in each of which components of the device are housed in one housing. The flame monitoring program may be recorded in a non-transitory computer-readable storage medium such as the above storage device 23. The above status values, the combustion information, and the like may be recorded in another storage unit such as a RAM, which is a volatile storage device, only for a certain period.

The combustion device 30 may be of a type including only the main burner 42 without the pilot burner 43. In addition, the combustion device 30 may be in a state in which the pilot burner 43 is always ignited. In this case, a flame detector for the main burner 42 and a flame detector for the pilot burner 43 may be prepared.

Modification 5

As a period for counting the number of discharge times N based on which the flame level FL is derived, a plurality of types of periods such as 0.1 seconds and 1 second may be prepared. In this case, the flame levels FL may be derived for the plurality of types of periods, and may be individually monitored by the flame level monitoring unit 21B. For example, a first flame level in which the period for counting the number of discharge times N is 0.1 seconds and a second flame level in which the period is 1 second may be derived and monitored. In this case, different predetermined periods Tth may be set for types of flame levels. Accordingly, the flame levels can be finely monitored.

Modification 6

Other fuels such as liquid fuel and gas-liquid mixed fuel may be used instead of the fuel gas.

RANGE OF THE PRESENT DISCLOSURE

Although the present disclosure has been described with reference to the embodiment and modifications, the present disclosure is not limited to the above embodiment and modifications. For example, the present disclosure includes various variations to the above embodiment and modifications that can be understood by those skilled in the art within the scope of the technical idea of the present disclosure. The configurations described in the above embodiment and modifications can be appropriately combined within a consistent range. 

1. A flame monitoring device comprising: an information acquisition unit configured to sequentially acquire a flame level indicating frequency of discharge of a flame detector caused by a flame of a burner; and a flame level monitoring unit configured to monitor the flame level sequentially acquired by the information acquisition unit; wherein the flame level monitoring unit is further configured to detect a sign of a flame failure of the flame by detecting an occurrence of a specific period during which a state in which the flame level is less than a predetermined threshold value continues for a length of time more than or equal to a predetermined first period and less than a second period, and the second period is a period having a length of time equal to or less than a period from an occurrence of the flame failure of the flame to the detection of the flame failure in a combustion system that controls the burner when it is assumed that the flame failure occurs.
 2. The flame monitoring device according to claim 1, wherein the flame level monitoring unit is further configured to execute a process of notifying that the sign is detected when the occurrence of the specific period is detected.
 3. The flame monitoring device according to claim 2, wherein the flame level monitoring unit is further configured to execute a process of notifying that the sign is detected when the number of occurrences of the specific period per certain period is larger than a predetermined number of times larger than or equal to two.
 4. The flame monitoring device according to claim 2, wherein the information acquisition unit is further configured to sequentially acquire flow rates of fuel and air that are supplied to the burner, and the flame level monitoring unit is further configured to notify of the detection of the sign along with flow rate information indicating a relation between the flow rate of fuel and the flow rate of air in at least one of the specific periods and a certain period traced back from the specific period based on the flow rates of fuel and air that are sequentially acquired by the information acquisition unit.
 5. The flame monitoring device according to claim 1, wherein the information acquisition unit is further configured to sequentially acquire combustion information including at least the flame level in the combustion system, and the flame level monitoring unit is further configured to: learn a relation between presence or absence of the occurrence of the flame failure and the combustion information by using, as training data, a variation in combustion information in a period traced back by a predetermined time from the actually occurring flame failure and a variation in combustion information for the predetermined time when no flame failure occurs from the combustion information sequentially acquired by the information acquisition unit; and derive a possibility of the occurrence of the flame failure based on the variation in combustion information for the predetermined time from the combustion information sequentially acquired by the information acquisition unit and the learned relation, and execute a process based on the derived possibility.
 6. The flame monitoring device according to claim 5, wherein the flame level monitoring unit is further configured to learn the relation by using a variation in combustion information in a period traced back by the predetermined time from the specific period actually generated from the combustion information sequentially acquired by the information acquisition unit as the variation in combustion information in a period traced back by the predetermined time from the flame failure.
 7. The flame monitoring device according to claim 5, wherein the process based on the derived possibility includes at least one of a process of notifying of the possibility, a process of notifying that the possibility is larger than a predetermined value, and a process of stopping fuel supply to the burner when the possibility is larger than the predetermined value.
 8. The flame monitoring device according to claim 3, wherein the information acquisition unit is further configured to sequentially acquire flow rates of fuel and air that are supplied to the burner, and the flame level monitoring unit is further configured to notify of the detection of the sign along with flow rate information indicating a relation between the flow rate of fuel and the flow rate of air in at least one of the specific periods and a certain period traced back from the specific period based on the flow rates of fuel and air that are sequentially acquired by the information acquisition unit.
 9. A non-transitory computer-readable storage medium storing a flame monitoring program for causing a computer to execute: an information acquisition step of sequentially acquiring a flame level indicating frequency of discharge of a flame detector caused by a flame of a burner; and a flame level monitoring step of monitoring the flame level sequentially acquired by the information acquisition step; wherein in the flame level monitoring step, a sign of a flame failure of the flame is detected by detecting an occurrence of a specific period during which a state in which the flame level is less than a predetermined threshold value continues for a length of time equal to or more than a predetermined first period and less than a second period, and the second period is a period having a length of time equal to or less than a period from an occurrence of the flame failure of the flame to the detection of the flame failure in a combustion system that controls the burner when it is assumed that the flame failure occurs. 